1) Field of the Invention
The present invention relates to an interface circuit for a card-type memory such as a secure digital (SD) card that is detachable and requires access by sectors, and to an application specific integrated circuit (ASIC) including the interface circuit, and an image forming apparatus including the ASIC.
2) Description of the Related Art
One approach to update software for equipment such as printers, copying machines, and multifunction peripherals (MFP) is to load the software from a memory card or download the software through a host interface of a network. However, in many cases, e.g., in field support, the host interface can not be used.
To allow the use of the host interface, some equipment is provided with a memory card interface. The memory card is handled in the same manner as random access memory (RAM). In other words, when the memory card is used, the interface does not require initialization. In addition, a program can be executed on the memory card. However, the memory cards have a problem in that they have low capacity of at most 4 megabytes, and they are not readily available in the market these days.
Japanese Patent Application Laid Open No. H11-242596 (see FIG. 1) discloses SD cards that can be used instead of the memory cards. The SD cards are attracting attention as portable media like floppy disks (FD). The SD card has a larger capacity per unit size, so that it is useful for recording and reproducing image data or audio data. If the access to the SD card is restricted to a read-access, a basic input/output system (BIOS) is not required. In addition, only required data can be read out according to the access from a central processing unit (CPU), and therefore, a program can be executed on the SD card without data being copied to a random access memory (RAM). If a communication error occurs, a communication speed is automatically reduced step by step to a speed at which no error occurs, then the processing is continued. Thus, it is possible to perform data communications without changing software and hardware.
However, in an SD card interface with a buffer size only by one sector, if a program extends over a plurality of sectors due to a jump instruction or the like, an overhead required for reading data from the card-type memory is largely affected, which causes an execution speed of the program to below.